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**Essay Questions**

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25. (2 pts) (transient) **Specific storage** represents the volume of water lost from a unit volume of the aquifer due to a unit drop in head. The loss of water is due to two factors. Describe the two factors.

26. (3 pts) (transient) Suppose you are building a MODFLOW model for a one year transient simulation. The purpose of the model is to simulate the effect of a new well. The well starts out in the **off** position (Q = 0). After four months, the well turns **on**. The well is on for four months and is then **off** for the last four months. Discuss how many stress periods you would use in this simulation. Also describe how you would distribute time step lengths within each stress period.

27. (3 pts) (modflow) With both the **river** and the **general head** packages in MODFLOW, the flow rate is a function of the head difference between the aquifer and the external source/sink. What is the key difference that distinguishes the river package from the general head package?

28. (3 pts) (bc) Suppose you are asked to review a ground water model developed by another company. The model is a local scale model to be used in designing a remediation system. You notice that the boundary conditions at the upstream and downstream ends of the model are specified head boundary conditions and the prescribed head values were interpolated from heads at observation wells. The other two boundaries are parallel flow boundaries. What would you discuss with the company regarding the **model conceptualization/setup**?

29. (3 pts) (stochastic) What is the objective of a **Monte Carlo** simulation? What are the basic steps involved?

30. (3 pts) (calibration) Discuss the problem of **model non-uniqueness**. What can be done to prevent model non-uniqueness?

31. (3 pts) (sustain) Describe the dynamics of what happens when a new set of wells is introduced. Explain how achieving a new state of equilibrium is a requirement for a **sustainable** aquifer management plan. Include a definition of **transitional storage** and **groundwater mining**.